Mosquitoes represent the major arthropod vectors of human disease worldwide transmitting malaria, lymphatic ﬁlariasis, and arboviruses such as dengue virus and Zika virus. Unfortunately, no treatment (in the form of vaccines or drugs) is available for most of these diseases and vector control is still the main form of prevention.

The limitations of traditional insecticide-based strategies, particularly the development of insecticide resistance, have resulted in signiﬁcant efforts to develop alternative eco-friendly methods. Biocontrol strategies aim to be sustainable and target a range of different mosquito species to reduce the current reliance on insecticide-based mosquito control.

In this review, we outline non-insecticide based strategies that have been implemented or are currently being tested. We also highlight the use of mosquito behavioural knowledge that can be exploited for control strategies.

Pesticide resistance is going to change rapidly our antibiotics and insecticides arsenal. In this scenario, plant-derived natural products are considered valuable candidates to reverse this negative trend. Growing research attention is focused on neem (Azadirachta indica, Meliaceae), exploring the utility of its products as insecticides and antibiotics.

In this review, we summarised the knowledge on neem oil and neem cake by-products in arthropod pest control, with special reference to mosquito vectors of public health importance. To the best of our knowledge, neem-borne products currently showed effective and eco-friendly features, including little non-target effects, multiple mechanisms of action, low cost, easy production in countries with limited industrial facilities. In particular, the potentiality of neem cake as ideal and affordable source of mosquitocidal compounds in anopheline and aedine control programmes is outlined.

Overall, we propose the employ of neem-based products as an advantageous alternative to build newer and safer arthropod control tools.

Experts have warned the Delhi government's fogging exercise is 'ineffective' in tackling the capital's growing dengue and chikungunya crisis.

They claim that there is no evidence to show that the government-led fumigation exercise is reducing the numbers of disease-spreading mosquitoes, with some data suggesting that the vectors have become 'resistant' to the chemicals used.

Dr Randeep Guleria, head of department of pulmonary medicine at the All India Institute of Medical Sciences (AIIMS), said that, at the very best, the fogging drive was merely a containment measure, rather than a preventative one.

He said: "The data to suggest that fogging actually decreases number of mosquitoes is not very strong.

"Fumigation is not a preventive measure but only a containment measure. It is a high-risk formula with only psychological effects. It makes people feel safer."

According to Guleria, there is data which suggest that mosquitoes have in fact become resistant to the chemical used in fumigation and may not die.

He continued: “Fumigation is not fool-proof. Dengue has to be controlled at the larval stage.”

Leader of House in SDMC and former South Delhi mayor Subhash Arya, said: “Fogging is mostly done outside the houses which can be effective only for five to 10 minutes and then it gets mixed in the air and, hence, there will be no impact on the mosquitoes.”

Meanwhile, doctors have issues a warning about the serious health implications to humans in the pesticide drive.

The fogging machines used by the municipal corporations in Delhi spray 95 litres of diesel mixed with insecticides in an hour.

According to doctors, one of the insecticides used for fumigation is malathion which can be hazardous for humans, especially for the vulnerable, young and elderly groups.

It's claimed that it can have chronic long term effects and can cause short term breathing problems and headaches in healthy people, with it posing an even greater threat to those with pre-existing breathing difficulties.

July 07, 2016

Based on several reports that Zika virus is spreading rapidly in Puerto Rico, federal officials yesterday recommended that the territory consider aerial spraying as part of a program to curb the mosquito populations that spread the disease.

Puerto Rico has reported spikes in Zika infections, and an update today from the US Centers for Disease Control and Prevention (CDC) shows that 506 more cases have been reported from affected territories since the previous week, most of them in Puerto Rico.

In other Zika developments, European researchers who sifted through travel-illness data found very few mosquito-borne illnesses in those who visited Brazil in the months that parallel the upcoming Olympic and Paralympic Games.

Resistant mosquitoes limit spray formula

CDC Director Tom Frieden, MD, MPH, said several independent sources indicate that based on current trends, thousands of pregnant women in Puerto Rico will be infected with Zika virus.

"The continental United States has been using aerial spraying for decades to reduce mosquito populations, and we urge the people of Puerto Rico to consider using the same proven and safe tactic," he said in a statement.

The CDC and the Environmental Protection Agency (EPA) are recommending spraying, which EPA administrator Gina McCarthy said is in line with integrated mosquito control recommendations for other parts of the United States. "We strongly encourage the people of Puerto Rico to consider aerial spraying as this approach is safe for people and a proven way of controlling the spread of mosquitoes that transmit diseases from Zika to dengue to chikungunya," she said.

The two agencies said they would help Puerto Rico implement an integrated mosquito control plan, with the CDC providing initial funding and technical support and the EPA providing technical and regulatory guidance. Plans include $500,000 in dedicated funding to safely get rid of discarded tires and other standing water sources and support for communities to use adulticides and larvacides.

For aerial spraying, Puerto Rico won't be able to use pyrethroid formulations, because studies earlier this year showed mosquitoes in the territory were resistant, the CDC said in its statement. The alternative product being considered is Naled, which has been used on the US mainland as recently as last year, including in Miami and Tampa, Fla. The same product has been used following hurricanes in Florida and was used in Puerto Rico in 1987.

The CDC said on Jul 1 that Puerto Rico received $5 million of $25 million from the agency to help states, cities, and territories battle the Zika virus.

Scientists acknowledge that the parasite is a formidable foe that has managed to evade global attempts to destroy it over six decades. Armed with the safe, inexpensive drug chloroquine and the powerful insecticide DDT, the WHO launched the Global Malaria Eradication Programme in 1955 with the goal to eliminate the disease within a decade.

Billions were spent in distributing the anti-malarial medicines, insecticide-treated bednets and fogging with DDT, but the parasite and mosquito survived new drugs, insecticides and habitat changes to continue to infect and kill people in 97 nations.

Over the past decade, the parasite is steadily developing resistance to every frontline anti-malarial drug.

The parasite is now so entrenched across most parts of India that it can be controlled only with a combination of drugs. India’s National Vector Borne Disease Control Programme (NVBDCP) rolled out the WHO-approved fast-acting combination called artemisinin combination therapy (ACT) in 2010. Under the national programme, ACTs are provided free for all, as are long-lasting insecticidal nets, which stay effective for three years and help in lowering transmission.

ACTs are made using artemisinin-based compounds in combination with other classes of anti-malarials. The ACT combination of artesunate and sulphadoxine-pyrimethamine (AS+SP), for example, is the first-line treatment for uncomplicated P. falciparum malaria. With cases of resistance to AS+SP reported in the northeastern states, the Centre gave its nod to the artemether and lumefantrine (ACT-AL) combination for use in the region in April 2013.

Finishing the job

Adding to the problem is the mosquitoes growing resistance to pesticides, the mainstay of vector (mosquito) control. The Anopheles mosquito has grown resistant to DDT and malathion, but is still sensitive to pyrethroid.

GSK’s malaria vaccine triggers the immune system to defend against P. falciparum when it first enters the human bloodstream and/or when the parasite infects liver cells. The vaccine, however, is only partially effective and at best can help control, and not eliminate, malaria. “The way ahead is rapid-diagnostic testing and using ACTs for treatment to prevent severe illness. That, along with the use of indoor residual spraying and long-lasting insecticidal nets in endemic areas, are the tools we know work against malaria,” says a Union Health Ministry official.

March 19, 2016

On an inexorable march across the hemisphere, the Zika virus has begun spreading through Puerto Rico, now the United States’ front line in a looming epidemic.

The outbreak is expected to be worse here than anywhere else in the country. The island, a warm, wet paradise veined with gritty poverty, is the ideal environment for the mosquitoes carrying the virus. The landscape is littered with abandoned houses and discarded tires that are perfect breeding grounds for the insects. Some homes and schools lack window screens and air-conditioning, exposing residents to almost constant bites.

The economy is in shambles, and thousands of civic workers needed to fight mosquitoes have been laid off. The chemical most often used against the adult pests no longer works, and the one needed to control their larvae has been pulled from the market by regulators.

A quarter of the island’s 3.5 million people will probably get the Zika virus within a year, according to the Centers for Disease Control and Prevention, and eventually 80 percent or more may be infected.

“I’m very concerned,” Dr. Thomas R. Frieden, the C.D.C. director, said in an interview after a recent three-day visit to Puerto Rico. “There could be thousands of infections of pregnant women this year.”

March 10, 2016

SAN JUAN, Puerto Rico — The advice is right there, on the website of the Centers for Disease Control and Prevention. To avoid contracting Zika, treat your clothing with an insecticide known as permethrin or buy apparel that is already treated with it.

If you live in or plan to visit Puerto Rico, there’s just one problem with that recommendation. The Aedes mosquitoes that transmit the virus on this Caribbean island have developed resistance to permethrin. The chemical isn’t working here.

And it’s not just Puerto Rico. Other places, including parts of Mexico, are reporting that Aedes mosquitoes are no longer quelled by permethrin, said Roberto Barrera, chief of entomology and ecology activity at the CDC’s dengue branch.

“It’s probably not going to work well in the places where it has been used as the main insecticide for many years,” Barrera told STAT in a recent interview. “You’re not going to be able to kill off most of the mosquitoes.”

The growing resistance to permethrin is a blow for public health authorities hoping to limit the damage Zika may wreak in Puerto Rico, where the virus is expected to spread widely and rapidly.

The first locally acquired Zika case was spotted here in late November. As of late last week, there were 157 confirmed cases — and doubtless many more in people who had no symptoms or were so mildly ill they didn’t seek medical care.

An insecticide, permethrin is toxic to mosquitoes but safe for use to protect people. While many people feel ambivalent or worse about insect repellants, permethrin has nevertheless gained a high degree of consumer acceptance.

CDC mosquito experts are in the process of trying to find effective alternatives for use in Puerto Rico.

March 02, 2016

On Nov 12, 2015, faced with the increased incidence of cases of microcephaly and the possible association with Zika virus, the Ministry of Health in Brazil declared a public health emergency. On Dec 5, the Brazilian Government decided that measures should be aggressively implemented to reduce the risk of exposure to Zika virus by eliminating the vector mosquito Aedes aegypti.

The strategy to eliminate the mosquito is based on pesticides (insecticides and larvicides) that have been applied since the dengue outbreak in 1986. Nevertheless, the results have been very disappointing. The incidence of registered dengue cases has increased, and in 2015 there were 1·6 million cases with 863 deaths (figure). Different insecticides (organophosphates and pyrethroids) and larvicides (organophosphates and growth regulators) have been successively used as a result of growing vector resistance.

Insecticide resistance is an example of evolutionary change, where the insecticide acts as a powerful selection factor that concentrates resistant mutants that were present in low frequencies in the original population.

Despite these negative results, the Ministry of Health in Brazil has intensified the same strategy to face the epidemics of Zika and chikungunya, by mobilisation of the armed forces to survey households, addition of larvicide to water supplies, and by the use of thermonebulisation as an attempt to control the adult vector; despite serious concerns regarding the larvicide pyriproxyfen (Malathion).

The Revolving Fund for Strategic Public Health Supplies in the Pan American Health Organization has prioritised the purchase of pesticides. The prescribed model of implementation is centralised, vertical, and does not consider the steep social gradient where clusters of microcephaly areis found in poor outskirts of cities, where sanitary conditions are bad.

Although official data point out that 92% of urban households in Brazil were connected to public water in 2010, there are 3 983 329 unserved households, and intermittent water supply, forcing the population to store water for everyday consumption, and favouring mosquito breeding. And only 28% of rural households are connected to public water.

The approach applied so far by the Government uses large resources on inefficient or unsafe vector control methods, instead of improving urban infrastructure and environmental sanitation, with a stable supply of potable water.

Relying on a chemical war against the vector tends to pacify the population with false security, while a broad programme for better sanitary urban conditions could generate social mobilisation and co-responsibility of the population. Improvement of sanitary conditions is a long-term investment in population health, while pesticide use will have to be repeated.

The Brazilian Association of Collective Health calls to stop the use of chemical products against A aegypti, especially in household water reservoirs, and prioritise sanitary measures.

May 17, 2014

Heath experts warn that mosquitoes in Vietnamese cities have exhibited an insecticide-resistance at the same time that climate factors have extended the dengue fever season year-round.

Mosquitoes carrying the virus have exhibited signs of resistance to several common common insecticides said Tran Thanh Duong, head of the National Institute of Malariology, Parasitology and Entomology during a Wednesday meeting in Hanoi.

Duong said the disease has killed at least four among the more than 8,000 people infected this year and will grow increasingly hard to manage since Vietnam hosts four strains of the virus.

People who develop immunity to one remain vulnerable to others, he said.

Duong said the disease has become active during all seasons due to climate and environmental changes.

Traditionally, the illness peaked in the south during June (the start of monsoon season) and in September in the north.

Duong said dengue fever has been considered an urban disease due to a dramatic surge of infections in large cities and rapidly urbanizing areas.

Health officials in Ho Chi Minh City, the country’s largest metropolis reported more than 2,600 dengue fever cases this year, up nearly 28 percent year on year.

They've also warned that the disease may see its peak turn, this year, in its three- to five-year cycle.

The city health department is conducting sterilization and larva destruction campaigns through June.

Meanwhile, a May 16 report says Vietnam is at risk of a triple pandemic of hand-foot-mouth disease, dengue, and measles. And a 58-year-old man, fond of raw pig's blood pudding and a dish including pig intestines and raw vegetables, has been hospitalized with parasitic worms in his brain. The National Hospital of Tropical Diseases gets 30 to 40 such cases a year.